The present invention relates to a frame structure for a vehicle comprising a reinforcing member which is provided in a main closed-cross section and cooperates with one of an outer panel and an inner panel to form a sub closed-cross section extending in a longitudinal direction.
Conventionally, a structure in which a crash can (a crash box) configured to be axially-compressively deformable is provided at a tip portion of a high-tensile steel-plate made front side frame and plural impact-absorbing mechanisms configured to be bendable initiatively are provided over a range from a midway portion of the front side frame to a rear end portion of the front side frame has been used to increase the impact energy absorption in a vehicle frontal collision, thereby achieving passenger's protection. In such impact-absorbing mechanisms, since an impact load absorbed through bending deformation of the front side frame shares most of the energy absorption after the axially-compressive deformation of the crash can, energy absorption characteristics through the bending deformation affects the EA (Energy Absorption) performance more than energy absorption characteristics through the compressive deformation.
In a frame structure disclosed in Japanese Patent Laid-Open publication No. 2016-113084, a first reinforcing member which cooperates with a main closed cross section to form five sub closed cross sections which are vertically adjacent to each other comprises a first partition wall portion including a first compression-side partition portion and a first tension-side partition portion and a second partition wall portion including a second compression-side partition portion and a second tension-side partition portion, a vertical distance between tension-side ridgeline portions facing each other is set to be smaller than a vertical distance between compression-side ridgeline portions facing each other, and when a difference between a lateral width of the first and second compression-side partition portions and a lateral width of the first and second tension-side partition portions at a front end portion of a front-side area is set to be smaller than a difference between a lateral width of the first and second compression-side partition portions and a lateral width of the first and second tension-side partition portions at a rear-half portion of the front-side area in a case where a load is inputted. Thereby, the tension-side ridgeline portions facing each other contact early after buckling of the frame happens, so that the respective partition wall portions cooperate with each other to constitute a truss structure on a tension side, thereby suppressing a sectional collapse caused by the bending deformation.
The frame structure of the above-described patent document can increase an allowable-limit load up to the plastic zone (area) of a material, so that the EA efficiency in the bending deformation of the frame properly increases. However, while the above-described frame structure of the patent document increases the EA efficiency due to the bending strength that the reinforcing member has, the axially-compressive deformation is not considered at all in this frame structure, so that the compressive strength that the reinforcing member has may not sufficiently contribute to the increase of the EA efficiency in the bending deformation of the frame. That is, if the impact load was absorbed by using the compressive strength of the reinforcing member in addition to the bending strength, the EA efficiency could be further increased and therefore the load absorption could be increased properly.